Phenylketonuria is an autosomal recessive disorder in which a genetic mutation causes a disorder of phenylalanine metabolism. Patients with phenylketonuria should be fed a low-phenylalanine diet. Infants and young children should be fed low-phenylalanine formula. Infants and toddlers who have already added complementary foods, the food selection is based on the principle of low protein and low phenylalanine, and need to control the intake of protein-rich foods such as meat, fish, eggs, seafood, offal, beans, etc.; rice-flour staple foods need to be appropriately limited, and low phenylalanine staple foods such as sweet potatoes, potatoes, taro, etc., can be chosen as substitutes. Low-phenylalanine dietary treatment should be continued at least until adolescence, and lifelong treatment is more beneficial to patients. Adult women should continue low-phenylalanine dietary treatment until delivery before pregnancy to avoid affecting fetal growth and development; it is recommended that blood phenylalanine should be controlled at 120 to 360 μmol/L. Families need to know the basics of phenylketonuria to help in the daily care of the patient, and once diagnosed, actively seek treatment.